in gcc we use __attribute__((interrupt("FIQ")))  for fiq handler in C.  what is the equivalent using armcc compiler?

I haven't much experience in using GCC, so there could be be some aspects of this feature I am not aware of.  However, I believe what you are looking for is "__irq", as in:

__irq void interruptHandler(void)
{
  ....
}

ARM Compiler armcc User Guide : 10.11 __irq

Although the name suggests its for IRQs, the generated code would also be compatible with FIQs.